The present invention relates to a gumming device.
The present invention may be used to advantage in the gumming of cardboard blanks on a cigarette packing machine, to which the following description refers purely by way of example.
U.S. Pat. No. 4,736,703 describes a cigarette packing machine on which blanks are fed along a straight path tangent to the lateral surface of a gumming roller rotating at constant speed and having a bottom portion immersed in a bath of gum. Between the bath of gum and the point at which the gum is applied to the blanks, a scraping device provides for evening the thickness of the layer of gum on the lateral surface of the gumming roller, which may have cavities for receiving given quantities of gum. If so, the scraping device is so arranged as to remove substantially all the gum off the lateral surface of the gumming roller, except for the gum inside the cavities, which is only applied to given portions of the blanks.
The above gumming device has several drawbacks. In particular, gumming rollers of the above type are particularly xe2x80x9cdirtyxe2x80x9d and call for frequent cleaning on account of the roller rotating inside the bath of gum; the gum in the bath tends to dry when the machine is stopped, by remaining in contact with the air with no provision for stirring; and roller gumming devices of the above type fail to reproduce the desired gumming pattern accurately, by failure of the scraping device to thoroughly clean the lateral surface portions of the roller corresponding to the gumfree portions of the blank.
To eliminate the above drawbacks, spray gumming devices have been proposed, as described in Patent EP-B1-601411. Such devices, however, have proved relatively expensive and unreliable on account of frequent clogging of the spray nozzles.
Furthermore, to eliminate the above drawbacks gumming devices disclosed in Patent WO-A1-0003814 (which is an earlier patent document, but published after the filing date of the present patent application) and in Patent WO-A1-8803844 were proposed. Patent WO-A1-0003814 and Patent WO-A1-8803844 disclose a gumming devices for applying gum to an article, wherein an article to be gummed is fed along a path tangent to a lateral surface of a gumming disk having an inner chamber communicating with a number of radial feed channels terminating at the lateral surface of the gumming disk; the gum is fed under pressure to the inner chamber to wet part of the lateral surface of the gumming disk via the feed channels.
The gumming devices disclosed in Patent WO-A1-0003814 and Patent WO-A1-8803844 have some drawbacks stemming from the fact that the feeding devices used in the above known gumming devices to fed the gum under pressure to the inner chamber of the relevant gumming disks do not allow controlling in a sufficient precise manner the feeding of the gum to the radial feed channels terminating at the lateral surface of the relevant gumming disks.
It is an object of the present invention to provide a gumming device designed to eliminate the aforementioned drawbacks, and which is also straightforward and cheap to produce.
According to the present invention, there is provided a gumming device for applying gum to an article as recited in claim 1.